Each year in the U.S., more than 100,000 electronic pacemaker systems are implanted to address the effects of cardiac arrhythmias. The pacemaker system can include a pulse generator as well as a lead with tip electrodes that deliver stimulation pulses to the cardiac tissue. To avoid open heart surgical procedures for pacemaker implantation, the lead is threaded through the vessels of the upper venous system, for example, via the subclavian vein to the superior vena cava (SVC), where a tip electrode is coupled to the endocardium within the right ventricular (RV) apex or right atrial (RA) appendage.
The cardiac pacemaker lead is commonly implanted under guidance of single plane fluoroscopy, which may be similar to other minimally invasive cardiac procedures, such as percutaneous catheterization and needle pericardiocentesis. In each of these procedures, the pacemaker lead, the catheter and the needle show high x-ray image contrast. However fluoroscopic guidance may suffer from poor soft tissue contrast, lack of depth information and the risks of ionizing radiation to both patient and health care staff. Accordingly, methods of catheter and needle guidance using ultrasound imaging have been investigated.
It is known that direct ultrasound visualization of a catheter or needle, particularly the tip, is difficult since these are specular reflectors that may appear only intermittently in a conventional ultrasound image. One approach to this problem is to track the catheter by attaching a piezoelectric transducer near the catheter tip which may act as a transmitter or receiver/transponder. For example, the catheter transducer may act as a receiver in the ultrasound field of an imaging transducer. The time of flight from the transmit pulse of the imaging transducer to its reception on the catheter transducer is recorded and used to inject a marker signal in the image at the appropriate depth.
It is also known to use the maximum signal received by the piezoelectric transducer during an ultrasound B-scan to determine the correct image line for the marker signal. For example, an Echomark catheter (Echocath, Princeton, N.J.) has been used with a real time 3D ultrasound scanner (Volumetrics Medical Imaging, Durham N.C.) for cardiac catheter tracking in three dimensions in animal studies. In such studies, spatial cross-correlation was used with stored receive beam profiles to achieve 1% measurement accuracy of the position of the catheter in three dimensions.
It is also known to guide a vibrating needle using a two dimensional ultrasound scanner, as discussed, for example, in Localization of Needle Tip with Color Doppler During Pericardiocentisis: In Vitro Validation and Initial Clinical Application, by Armstrong et al., American Society of Echocardiography, 2001, 0894-7317/2001. Other techniques are also discussed, for example, in U.S. Pat. Nos. 5,329,927; 5,421,336; 5,425,370; 5,967,991; and 5,968,085, the disclosures of which are hereby incorporated herein by reference.